Previous experience using a voltmeter/multimeter is helpful, but not required. A basic knowledge of how to work with bacteria is also needed to complete this science fair project. Consult the Microbiology Techniques and Troubleshooting guide for information on how to conduct microbiology experiments.

Material Availability

A microbial fuel cell and other specialty items are needed. See the Materials tab for more details.

Cost

Average ($50 - $100)

Safety

Be sure to wear the gloves supplied with the kit when handling the microbial fuel cell’s electrodes (its cathode and anode). The electrodes are made of a conductive material called graphite fiber and should not be placed near electronics or power plugs, or have their fibers dispersed in the air. Use sterile technique when growing the bacteria. Read the Microorganisms Safety Guide before starting any experiments. SRC approval may be necessary. Adult supervision is recommended.

*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.

Abstract

Topsoil is packed with bacteria that generate electricity when placed in a microbial fuel cell (MFC). Because such bacteria-laden soil is found almost everywhere on Earth, microbial fuel cells can make clean, renewable electricity nearly anyplace around the globe. As natural resources are being depleted, scientists' attention has shifted to pursuing alternative energy sources, such as MFCs, even more than before.

A microbial fuel cell, also known as a biological fuel cell, is a device that can use microbes to generate electricity. An MFC has two electrodes and an area that separates the electrodes (called a membrane). For an MFC to function, electricity must flow into one electrode and leave the other electrode. How is this accomplished? It has to do with the bacteria in the MFC. Some types of soil bacteria can help generate electricity. These bacteria, known as electrogenic bacteria, include the Shewanella species, which can be found in almost any soil on Earth and are shown in Figure 1, and the Geobacter species, which prefer living in soil deep underground or even under the ocean, where no oxygen is present. The soil bacteria eat what is in the soil, such as microscopic nutrients and sugars, and in turn, produce electrons that are released back into the soil. Electrons are subatomic particles that have a negative charge. These electrons can be harnessed and used to create electricity, which is a form of energy.

Figure 1.
This is a high-magnification image of Shewanella bacteria, specifically the species S. oneidensis. The bacteria are the cylindrical-shaped rods scattered in this image. (The other parts of the image are ice pieces that the bacteria were submerged in to take this picture.) (Image credit: PLoS Biology)

In an MFC using these soil bacteria, one electrode (specifically the anode) is buried down in damp soil. Down there, the bacteria multiply and cover the electrode (creating a biofilm on it), supplying it with a lot of electrons. At the same time, the other electrode (called the cathode) is placed on the top of the soil, leaving one of its sides completely exposed to the air. Electrons from the bottom electrode travel up a wire to the top electrode and, once there, they react with oxygen (from the air) and hydrogen (made by the bacteria as it digests nutrients in the soil) to create water.

What do you think happens to the quantity of bacteria in the MFC as the power output increases? Does the number of bacteria, increase, decrease, or stay relatively stable? One way to investigate this would be to take a swab of the soil at the beginning of the experiment and grow the bacteria from the swab, and then take a swab when the power output is much greater and grow the bacteria from that swab. Do you see more bacteria growing on the nutrient agar plate from the second swab taken? Do you see different types of microbes growing? To learn how to set up the microbial fuel cell and take power output measurements, see Science Buddies' science project ideas
Turn Mud into Energy with a Microbial Fuel Cell — and a Dash of Salt
and
Powered by Pee: Using Urine in a Microbial Fuel Cell. For an idea of how to take bacterial swabs and grow them on agar plates, see Science Buddies' science project idea
Is That Really Bacteria Living in My Yogurt?
(Note:Shewanella bacteria can be aerobic [they need oxygen] or anaerobic [they grow without oxygen], and Geobacter bacteria are anaerobic. Knowing this, why do you think an anaerobic chamber might be ideal for doing this experiment?).

APA Style

Science Buddies Staff.
(2015, March 20).
How Do Bacteria Produce Power in a Microbial Fuel Cell?.
Retrieved August 2, 2015
from http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_p032.shtml

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Materials and Equipment

This is an abbreviated project idea, which means you will have to write your own experimental procedure and use it to create your own materials list. In general, think about the fact that you will need a microbial fuel cell (available from the Science Buddies Store), mud, petri dishes with agar for growing your bacteria, and other bacteria growing supplies. Bacteria growing supplies are available from online vendors like Carolina Biological Supply Company. The other Project Ideas linked to in the Background tab can help you figure out your procedure and materials list.

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